Amplifier



L.. E. BARTON Aug. 6, 1935. l v

AMPLIFIER Filed Dec. 29., 1933 vGoflr/a'oL e/D vous: o

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V pliners arefgcommonly; utilizediin;place@` Patented Aug. 6, 1935:5115115:

f-Mysinyent ,n.relatesf to amplifiers and particu: larlv to amplifiers,such-,ias athosegofr. the ,-ftriggerlj type, adaptedrgto control,electricalfdeyicea l .1 @Atv the presenti-timer;e1eetricgdischarseltube am,- fame-- chemicalllelays.`A @In the@iftriggerf typeaofiampliner. fithegoutpu of; the jfamplierlf' suddenlychangesV to, acertain` aluefinfresponse vt a prei determined change;.invvoltage :applied 'to the.; amt-i; pliferinput circuit.Triegerfiamplifiers:arefes: peoiallwtuseulwinfcircuits:requiring:,anonfand oir relayiaetienrsueh-:aszloavelmroiindisupioression circuits in radio receivers, and`Ytheliirreplaemg much moref sensitive and. eliabl than` rnef:hanicah:re-.-

proved :i LA further .,obieotiofnmy"invention-i aimprovoed.ramplifier-ofthe,ftrggertY me becmanufaoturedyatiaflow costa i`Aetill further;object;ofmyiinventionust 1p vdeanivimprovedftriegeramplerfwhich may be Controlled by changesinalternatine. current f; the. `prefer embodiment ggorniyginvention;llutilize. en eleotliopdisohareetubeofthenentode type in combinationwitharectiner. circuit s oconneotedV :that it leoneses @the i:eontrolrfgridf offV the pentodet-to beoomeibiesedmoreneeativelyaasthealternetingfieurrent output-o helpento e inereeses. i4 n i n 1r,

`Tlhe.pentodo is i perated With-1a ylow.. Qltaeeepplied to its \,anede 5whereby, the l 1v gain: of v the pentodeincreasesas the anode; oltage`increases. The oheneeein aaode,f,vo1tageisobteinediabyyinserting aresistorinthe,anode;` circuitso that a largefplate lenfreint invthe.pentodei eausesa llarge voltage drop across the resistor and acorrespondto. rovde typewhleh the-pent de cooed i With theoutputeireuit. Y to the reotier. Circuiti-e predetermined voltage.applied to the pentodes ieontrol grid-causes ,the control grid to.become more-negative whereby; the plate currentpdecreases andyahighervoltage is applied tothe anode ofythefpentode.` vIYhiS; in: creases thegain of the pentode, the control grid becomes still morenegative,pand;the 1:gainlfis further increased until` the` decrease in rgain4 caused by the negative biason then-,controlfgridequals theincrease in :gain 1 `caused fby; the t increase in v oltagegappliedtotheanode v Other objects,v `featuresfand advantages ofglmy invention willappearl fro-m the -Afoliowingi` description taken infconnecton withkthe`accompanying drawing in which, f

a y y N. J., assignm-- droJ Qorpprationfo America,v al orporation tDelawar t New York,` N.

ateristis of and A#the secondarywindngs "are f tned i tol that frequencyf by lneansbffcondensers 'f 43 and 4 5 Q respectively] S4 jl',` j "j .iyif henan alternating voltage ise impressed upon the Iamplinerf l'inputlfcr'cu-it, f' it is amplified inthe pentode sectionv9Vandthe"anfiplied*output; of `this Isection isltransferred throughtheftransformer 35 :and: impressed? upon the-*elements A5' and" 1 offthe? diode 'lrectif-ieri The; amplied energyisimpressedupon Asaidrectifier elements through afco'nductor V4.1 which connectstheldiodeplate 15Jtoone-.eterminal of thefsecondary windiing 4|, andthroughvaiconhection'fffrom-the cathode v'l 'tov the othex=.=termina1Aof the'isecondary 41,*1whi'ch connection may Abe tracedf'froni thecathode 1 through iaself` .biasing vresist'or'fd 1' to ground,` throughground to 'the llower :terminali of a resistorl5I`fv(whch may have a`resistance off the orderfof one megohm) and through thev resistor 5 If'to the said 'other terminal fof the secondary.` 4L

The sole function of the diode rectifier 3 is to increase the negativebias on the control grid I3 of the pentode section when -energy isimpressed upon the amplier input circuit. Since a flow of currentthrough the diode rectifier causes the upper end of the resistor 5I tobecome negative, the control grid I3 also becomes more negative becauseof its connection to the negative end of the resistor 5I through a highimpedance resistor 53.

The self biasing resistor 49, the resistor 5I and the plate resistor 31are preferably shunted by condensers 55, 51 and 59, respectively, forbypassing alternating current having the frequency of the input voltage.

It will be apparent from the foregoing description that as soon as analternating control voltage is impressed upon the input circuit of thepentode 9, the control grid I3 of thel amplifier becomes more negativebecause of the current ow through the circuit of the diode.

It should be noted that the change in bias on the control grid I3depends, to a certain extent, 1

upon the voltage drop produced in the selfbiasing resistor 49, sincethis voltage drop is in series with the voltage drop along the resistor'5I of the diode circuit. That these voltage drops are in series will bemade evident by tracing the direct current path of the pentode sectioninput circuit. It may be traced from the control grid I3 through thesecondary winding 25, the high impedance resistor 53, through the diodecircuit resistor 5I to ground, through ground to the self-biasingresistor 49, and through the selfbiasing resistor 49 to cathode 1.

When there is no alternating voltage being impressed upon the amplifierinput circuit, the plate current of the pentode 9 is large, since theonly negative bias on the control grid I3 is that due to theself-biasing resistor 49, and this negative bias is comparatively small.Consequently, there is a large voltage drop in the plate resistor 31,whereby 'the upper end of resistor 31 is at a comparatively low positivepotential with respect to ground. This potential may be supplied throughan output circuit 6I to a circuit or device (not shown) to be controlledby the alternating voltage input. At the same time, the gain of thepentode 9 is low because of the low voltage on its anode I9.

As soon as an alternating voltage is impressed upon the input circuit,the amplifier 9 supplies signal energy to the diode 3, the voltage dropin the diode circuit resistor 5I increases the negative bias on thecontrol grid I 3, wherebythe plate current of amplifier 9 decreases andthe upper end of the plate resistor 31 becomes more positive withrespect to ground. Thus a higher voltage is applied to the outputcircuit 6I It will be apparent that, at the same time, a higher voltageis applied to the anode I9 of the pentode.

It should be noted that although the decrease in plate current tends tocause a reduction in the biasing voltage drop across the self-biasingresistor 49, the increased negative bias provided by the current iiowthrough the diode circuit resistor 5I is much greater than any decreasein bias due to reduction in plate current.

The above described action of the diode-pentode circuit whereby theupper end of plate resistor 31 becomes less negative in response to a.voltage impressed upon the input circuit is preferably made a triggeraction by giving plate resistor 31 a proper resistance value. Thistrigger action depends upon the fact that the increase in gain caused bythe increase in the plate voltage is greater than the decrease in gaincaused by the increase in negative bias on the grid. In practice, a tubeof the type known as RCA 2B? has been found satisfactory for use as thetube I.

Figure 2 shows a family of plate curves for a particular vacuum tubehaving the characteristics which are preferred in practicing myinvention. The operation of my amplifier will be better understood byreferring to the load lines Ri and Rz drawn through the plate curves,the load line Rr being for a plate load of 25,000 ohms and the load lineR2 being for a plate load of 50,000 ohms. For the purpose ofexplanation, it will be assumed that the plate load is equal to theresistance value oi' the plate resistor 31.

Under the condition of no input voltage to the amplifier, there is onlya small negative bias on the control grid I3 and the plate current iscorrespondingly high, whereby the voltage drop in resistor 31 is sogreat that the pentode 9 is operating at a very low plate voltage. Atthis low plate voltage the amplification of the pentode is comparativelylow, as will be seen by referring to the intersection of the load lineR1 with the plate curve for a bias voltage of minus one volt. It will beapparent that, if the voltage impressed upon the input circuit swingsthe grid one volt each side of the bias potential, that is, between zerovolts and minus 2 volts, there is a compartively small change in theplate voltage, as indicated by the spacing between vertical lines 63, 65and 61.

As previously explained, the input voltage causes the negative bias ofthe grid I3 to increase. Assuming the input voltage has increased thebias to minus 3 volts. it will be seen, by referring to' the spacingbetween vertical lines 61, 69 and 1I,

that a grid swing of one 'volt each side of the bias voltage causes agreater change in plate voltage than was caused by the same grid swingat the lower bias potential. A further increase in negative bias on thecontrol grid I3 causes the tube amplification to increase still furtherand the output voltage may increase very rapidly (depending upon timeconstants of the circuits of condensers 59 and 29) up to a certainpoint. The curves show that as the bias increases to some value beyondthe region minus of -5 volts, the change in plate voltage for a givengrid swing begins to decrease, that is, the amplification ofthe'lpentode 9 begins to decrease. In other words, at this point theincrease in amplication due to the increase Vin plate voltage becomesless than the decrease in amplification due to -the increase in negativebias on the control grid, and the amplifier has reached a stablecondition where the output voltage is a maximum.

The operation of the amplier along the load line R2 is the same asdescribed above except that for the higher load resistance a greatervoltage input is required to trigger oi the amplifier. This is because agiven input will cause a smaller change in plate voltage than in thecase where a smaller load resistance is used, as will be apparent fromthe curves. I

It will be understood that in place of the double tube shown in Figure1, separate pentode and diode tubes may be employed.

Various other modifications may be made in my invention withoutdeparting from the spirit and scope thereof and I desire, therefore,that only such limitations shall be placed thereon as are necessitatedby the prior art and set forth in the appended claims.

--I climfasfmYmVm-OD? I'rrc bihaitionfanelectric discharge device av g`an 1n `t ircuitandan output circuit,

, .device,havingfaplurality of electrodes including a controlgfridlandan anode and having the characteristic that at low anodevoltages its gama-increases with increase of anode voltage. means forapplying a negative bias to said control grid means for increasing saidvnegative bias in response to an increase in alternating voltage appliedto said input circuit, and a resistor in said output circuit in serieswith said anode whereby the anode voltage increases as said control gridbecomes more negative.

2. In combination, an electric discharge device having an input circuitand an output circuit, said device having a plurality7 of electrodesincluding a control grid and an anode and having the characteristicthat. over a certain voltage range, the gain of said device increaseswith increase in voltage applied to said anode, a resistor in serieswith said anode, and means for making said control grid more negative inresponse y to an increase in alternating voltage applied toincrease ingain caused by the resulting incrase in anode voltage.

3. In combination, an electric discharge device having an input circuitand an output circuit, said device having a plurality of electrodesincluding a control electrode and an anode and having the characteristicthat, over a certain voltage range, the gain of said device increaseswith increase in voltage applied to said anode, a rectifier having aninput circuit and an output circuit, said rectier input circuit beingcoupled to said rst output circuit, said rectier output circuit being socoupled to said first input circuit that said control electrode becomesmore negative in response to an increase in the alternating currentoutput of said discharge device, a resistor in series with said anode,and means for coupling a work circuit to said resistor.

4. Apparatus according to claim 3 characterized in that said dischargedevice has the further characteristic that over said certain range thedecrease in gain caused by said control electrode becoming more negativeis less than the increase in gain caused by the resulting increase inanode voltage.

5. A trigger amplifier comprising a vacuum tube of the suppressor gridtype. Said tube having a plurality of electrodes including a controlgrid and an anode. said tube having an input and an output circuit, a.rectifier, means including said rectifier for giving said control grid anegative bias which increases in response to an increase in alternatingcurrent output appearing in said output circuit, and means in the anodecircuit of said tube for increasing the voltage applied to said anode inresponse to a reduction in the plate current of said tube.

6. An amplifier according to claim 5 characterized in that the voltageapplied to said anode has a value such that an increase in said voltagecauserJ an increase in the gain of said tube.

7. In combination, an electric discharge device having a plurality ofelectrodes including a pair of principal electrodes and a thirdelectrode, means for .producing a direct current flow between saidprincipal electrodes, means for applying a biasing potential to saidthird electrode in accordance with a ow of alternating current betweensaid principal electrodes whereby said direct current flow is varied,and means for controlling the voltage across said principal electrodesin accordance with said direct current iiow. said electric dischargedevice having the characteristic that its gain increases with increaseof voltage across its 4principal electrodes.

8. In combination, an electric discharge device of the pentode typehaving a pair of principal electrodes, a control grid, and two auxiliarygrids, means for producing a unidirectional current now between saidprincipal electrodes, an input circuit connected to said control gridand one of said principal electrodes whereby an alternating voltageimpressed upon said input circuit will produce an alternating currentcomponent in said unidirectional current flow, means for applying abiasing potential to said control electrode in accordance with saidalternating current component whereby the direct current component ofsaid unidirectional current iiow is varied, and means for controllingthe voltage across said principal 4electrodes in accordance with saiddirect current component.

9. In combination, an electric discharge device of the pentode typehaving a pair of principal electrodes, a control grid, and two auxiliarygrids, means for producing a unidirectional current flow between saidprincipal electrodes, an input circuit connected to said control gridand one of said principal electrodes whereby an alternating voltageimpressed upon said input circuit will produce an alternating currentcomponent in said unidirectional current flow, means for biasing saidcontrol grid an increasingly negative amount in response to an increasein said alternating current component whereby the direct currentcomponent of said unidirectional current flow is decreased, and aresistor connected in series with said principal electrodes whereby thevoltage applied across said principal electrodes increases with decreasein said direct current component.

10. In combination, an electric discharge device having a plurality ofelectrodes including a pair of principal electrodes and a thirdelectrode, said device having pentode characteristics, means forproducing a direct current flow between said principal electrodes, meansfor applying a biasing potential to said third electrode in accordancewith a ow of alternating current between said principal electrodeswhereby said direct current iiow is varied, and means for controllingthe voltage across said principal electrodes in accordance with saiddirect current flow.

11. In combination, an electric discharge device having a plurality'ofelectrodes including a pair of principal electrodes and a thirdelectrode, said device having', the characteristic that its curve ofplate current plotted against plate voltage is concave downward, meansfor producing a direct current iiow between said principal electrodes,means for applying a biasing potential to said third electrode inaccordance with a flow of alternating current between said principalelectrodes whereby said direct current flow is varied, and means forcontrolling the voltage across said principal electrodes in accordancewith said direct current ilow.

12. A trigger amplier comprising a vacuum tube having an amplifiersection and a rectier section, said amplier section including a controlelectrode and having a plate circuit including a series resistor, abiasing circuit including said rectier section, means for transferringenergy 5 from said plate circuit to said biasing circuit, and means4including a resistor in said biasing circuit for increasing thenegative bias of said control teristic that its amplifying abilityincreases with an increase in plate voltage.

LOY E. BARTON.

